1. Field of the Invention
The present invention relates to release mechanisms for loaded straps. More particularly, it relates to a controllable release for a parachute riser.
2. Discussion of Related Art
In parachute applications, it is desirable to have a quick release to separate the harness from the parachute. Different mechanisms have been used for such a purpose. Originally, a parachutist had to cut the webbing of the risers connecting the parachute to the harness. Early mechanical connections were difficult to use when the webbing was under tension, such as during flight. U.S. Pat. No. 4,337,913, entitled “Means for Releasably Attaching Strands”, incorporated herein by reference, disclosed a novel release mechanism which was easily operable, particularly for webbing under tension.
The release mechanism, commonly called a three ring release, consists of several connected strands of webbing, each ending with a ring. The rings are sized so that each can pass through the next larger one. The rings are passed through each other to hold each in place. The smallest ring is held by a loop of string. Each ring forms a lever and a fulcrum for the next ring, providing a mechanical advantage such than a small force is needed to disengage the string loop in order to release thousands of pounds of suspended weight on the mechanism. Typically, the string loop on the three ring release is held in place by a plastic coated wire cable extending through the loop on the back side of the riser webbing. In order to release the riser, the parachutist pulls the wire cable a couple inches so that the end passes through the string loop. The release of the string loop in turn releases the smallest ring, then the next, then the next thus disengaging the mechanism and separating the webbing.
While the three ring release is an excellent mechanism for a quick, easily operable release of risers by a parachutist, it is not easily adaptable for use in unmanned cargo drops. A remote linear actuator could be used to pull the cable. However, there are disadvantages in using a remote linear actuator. The size of an actuator for pulling the cable several inches makes mounting of the actuator a concern. A cable housing is necessary to prevent kinking or binding of the cable, which would prevent movement. The inherent friction between the housing and the cable requires a higher level of force to pull the cable than with the current invention. Additionally, even with a hard cable housing, the cable can kink at the point where it contacts the string loop due to forces on the loop, particularly when high weights or g-forces are encountered. The detent formed at the loop contact point can require a very high actuation force to pull the cable, making a release impossible. A solid metal pin could solve the detent problem but cannot be used at the end of the cable. The flexible nature of the riser would require a very short pin to prevent interference. A short pin could result in premature release. The cable is designed to be pulled several inches to prevent premature release. With a short pin any tension could cause the pin to be pulled prematurely. Therefore, a need exists for a quick release mechanism which can be used for unmanned operation.